1. Field of the Invention
This invention relates to semiconductor chip speed performance and more specifically to the limitation on chip speed performance which occurs as a consequence of a limited heat removal ability. More particularly, this invention relates to the maximum clocking rates which are imposed on chips fabricated in some of the popular technologies as a direct consequence of limitations in the rate at which heat can be removed from a chip.
2. Description of the Prior Art
The performance of some chips (especially VLSI chips) is bounded by the heat removal ability of their packages. Heat generation and removal is a problem accounting for the maximum clock rates specified for some VLSI chips. It is desirable to make these chips run faster, while staying within the heat removal limits of conventional packages.
One solution currently being pursued in the art is to cool the chip package using an external cooling device. Such a scheme has been used by Everex Systems, Inc. for the Intel 80486 microprocessor CPU chip that, although specified to run at a maximum of 25 MHz clock speed, achieves a clock rate of 50 MHz. The Everex scheme employs a product known as Icecap produced by Velox Computer Technology Inc., that cools the CPU chip to 0.degree.. This is described by Michael Fitzgerald in "Everex set to show 50-MHz PC" in Computerworld, Vol. XXIV, No. 41, at page 4 (Oct. 8, 1990).
In U.S. Pat. No. 4,670,837, a microprocessor controls the clock frequency based on the present rate of required microprocessor activity. However, the speed performance of the microprocessor is not improved. Variation of the clock frequency is used to save power (i.e., battery life), not to improve chip speed performance.
In "Intel to Introduce 20-MHz Chip Set", InfoWorld, Vol. 12, Issue 42, page 5 (Oct. 15, 1990), Nico Krohn described a new chip set intended for the laptop computer market in which power management features are built into the microprocessor. In order to conserve battery life, every piece of logic can be powered down. Again, the focus is on battery life and there is no apparent speed performance gain as a consequence of any of the powering down.
Intel Corp. has also published that it intends to introduce a dual-clock microprocessor (See Jim Nash, "Dual-clock 486SX: Bonanza for Intel?", Computerworld, page 89 (Aug. 5, 1991). It appears that there will be a static allocation of the two clock frequences to the tasks inside the chip. Functions such as direct memory access will run at the lower clock frequency while massive computations will run at the higher clock frequency. While the apparent focus here is on heat dissipation, the clocking rate of each circuit does not vary over time, so the maximum clocking rate for each circuit is still determined by the maximum heat dissipation rate from that circuit.